java设计模式之享元模式

概念：就是说在一个系统中如果有多个相同的对象，那么只共享一份就可以了，不必每个都去实例化一个对象。
Flyweight(享元)模式中常出现Factory模式。Flyweight的内部状态是用来共享的,Flyweight factory负责维护一个对
象存储池（Flyweight Pool）来存放内部状态的对象。
Flyweight的关键思路,在于:
新建对象时:先到hashtable中进行获取-->判断取得对象是否为空-->若是,则新建此对象,且放回hashtable -->若存在,则共享原来
的对象.

实例代码：

public interface Car {

    public void showCarName();
}

public class BMWCar implements Car {

    private String name;
    public BMWCar(String name){
        this.name=name;
    }
    public void setName(String name){
        this.name=name;
    }
    public String getName(){
        return this.name;
    }
    @Override
    public void showCarName() {
        // TODO Auto-generated method stub

        System.out.println("I am BWM car.");
    }

}

public class FordCar implements Car {

    public String name;

    public FordCar(String name) {
        this.name = name;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public void showCarName() {
        // TODO Auto-generated method stub

        System.out.println("I am a Ford car.");
    }

}

import java.util.Hashtable;

public class FlyWeightFactory {

    public static Car car;
    private static Hashtable<String, Car> carPool = new Hashtable<String, Car>();

    public static Car getCar(String name) {
        if ("BMW".equals(name)) {
            car = carPool.get(name);
            if (car == null) {
                car = new BMWCar("nan");
                carPool.put(name, car);
            }
        } else if ("Ford".equals(name)) {
            car = carPool.get(name);
            if(car==null){
                car=new FordCar("xi");
                carPool.put(name, car);
            }
        }
        return car;
    }
    public static int getNumber(){
        return carPool.size();
    }
}

public class test {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Car car,car1,car2;
        car=FlyWeightFactory.getCar("BMW");
        car.showCarName();
        car1=FlyWeightFactory.getCar("Ford");
        car1.showCarName();
        car2=FlyWeightFactory.getCar("BMW");
        if(car==car2){
            System.out.println("we are the same car.");
        }else{
            System.out.println("we are different car.");
        }
        System.out.println(FlyWeightFactory.getNumber());
    }

}

运行结果：

I am BWM car.
I am a Ford car.
we are the same car.
2